In recent years, keyboardless devices have become widely used that include smart phones and tablet-type devices such as a slate PC (Personal Computer) and an iPad (trademark). However, such keyboardless devices are not implemented with a character input interface that has a competitive operational feeling like a QWERTY-type physical keyboard, which is one of the most significant disadvantages for a user who needs to input a long passage.
For portable terminals such as a smart phone and the like, an input interface using a numeric keypad is most widely used that may be implemented with a touch panel or a physical keypad. If the number of types of characters is greater than the number of keys displayed on a screen, a key is assigned with multiple character types where a character is selected by pushing down the key one or more times. For example, a ten-key numeric keypad is displayed on a screen in which a key labeled with “2” has “A”, “B” and “C” assigned, with which one of the characters is selected by pushing down the key for a predetermined number of times.
Also, iPhone (trademark) is provided with an interface called “flick input”. With flick input, if a predetermined key is pushed down, characters assigned to the key are displayed on the left, right, top and bottom of the key.
For example, a ten-key numeric keypad is displayed on a screen in which a key labeled with “2” has “A”, “B” and “C” assigned, and if “A” is pushed down, “B” and “C” are displayed on the left and top of “A”, respectively. By lifting up the pushing finger at the position of one of the keys, the character type at the position is selected. Flick input can make the number of key pushes fewer than the method of selecting a character by multiple pushes.
The input methods described above allow input with one hand, which may be suitable for input operations during travel such as a train ride or for input of a short sentence. However, as portable terminals become smaller and so do character input areas on the terminals, operability of the keys become worse, especially when inputting a long sentence.
As for tablet-type devices, comparatively larger touch panel displays, such as a 10-inch type, are usually adopted, on which a software keyboard, for example, a QWERTY-type full keyboard, is displayed.
If such a software keyboard is displayed on a tablet-type device with a practical size, the keyboard may occupy a large display area on the screen, which makes it difficult to view an application display.
Regarding this matter, there is a technology for key inputs that detects positions of fingertips on a virtual keyboard. For example, fingertips of an operator are captured using two cameras, and three dimensional positions of the fingertips are detected from the captured images, with which keys on the virtual keyboard corresponding to the positions are determined (Patent Documents 1 and 2).